Triply Periodic Minimal Surfaces Mullite Structures for Humidity Detection

Three-dimensional-printed complex mullite structures based on triply periodic minimal surfaces (TPMSs, namely, Schwartz and Gyroid) with two different thicknesses (Schwartz 1 and Gyroid 1–4 mm, Schwartz 2 and Gyroid 2–6 mm) were fabricated and tested as humidity sensors. The samples were sintered at 1450 °C and tested in the range from 0% to 89% relative humidity (RH) at room temperature to evaluate the effect of geometry and thickness on humidity sensitivity. After water vapor exposure at room temperature, the response was 2.84 under 89 RH% for the Schwartz 1 structure (1.36 for the Schwartz 2 structure) and 1.21 for the Gyroid 1 structure (7.00 for the Gyroid 2 structure). The results showed that, at 89% RH, the best response of the sensors was achieved for the Gyroid 2 structure. Sensors exhibit good repeatability, and there was no interference in the presence of other gases.